1. Field of the Invention
This invention generally relates to a seat slide device, and more particularly, to a vehicle seat slide device for sliding a vehicle seat relative to a vehicle floor by driving a motor as a power source.
2. Discussion of the Related Art
Heretofore, as seat slide devices for vehicles, there have been known those of the constructions described in Japanese unexamined, published patent applications No. 9-142181 and No. 11-208322 and United States patent application publication No. US2006/0226674 A1 (equivalent of Japanese unexamined, published patent application No. 2006-290131) hereafter referred to respectively as “first to third patent documents”. Each of these devices is provided with a pair of left and right lower rails secured to a vehicle floor and a pair of left and right upper rails slidably supported along the lower rails and supporting a vehicle seat.
Each lower rail has a nut member fixedly held therein, while each upper rail has a screw shaft rotatably held and extending in a forward-rearward direction and a drive mechanism for driving the screw shaft. The screw shaft is in screw-engagement with the nut member. By operating the drive mechanisms to rotate the screw shafts, the upper rails are slidden to move in the forward-rearward of the vehicle relative to the lower rails. With the slide movement, the position of the vehicle seat held on the upper rails is adjustable in the forward-rearward direction of the vehicle.
The drive mechanism described in each of the first and second patent documents is composed of an electric motor and two reduction sections each for reducing the rotational speed of the electric motor and for converting the direction in which the rotational power is transmitted, from one direction into another. The reduction sections are respectively attached to the left and right upper rails through respective brackets holding the reduction sections. The electric motor is held on one of the reduction sections with its rotational shaft extending in a width direction (i.e., transversely of the rails). The rotation of the electric motor is transmitted to the other reduction section not holding the electric motor, through a rod (transmission shaft). In the device described in the third patent document (i.e., the US publication), a drive reduction gear mechanism for reducing the rotational speed of an electric motor is united with the electric motor, and direction conversion gear mechanisms each for converting the transmission direction of rotational power are arranged on left and right sides one for each side. These direction conversion gear mechanisms are respectively attached to the left and right upper rails through respective brackets holding the reduction sections. The electric motor and the drive reduction gear mechanism are arranged on an mid portion of a transmission shaft which drivingly connects the left and right direction conversion gear mechanisms. The transmission shaft is coupled to an output gear of the drive reduction gear mechanism, so that the rotation from the electric motor is transmitted to the left and right direction conversion gear mechanisms at a reduced rotational speed.
Japanese unexamined, published patent applications No. 9-207632 (hereafter referred to as “fourth patent document”) describes a seat slide device of the same construction as those described in the first and second patent documents. In the device, a flexible cable is used in place of the rod (transmission shaft) used in the first and second patent documents.
In the seat slide devices disclosed in the first to third patent documents, it may take place that the axes for the driving rotations which are inputted to the reduction sections or the direction conversion gear mechanisms attached to the left and right upper rails deviate from each other in the forward-rearward direction (occurrence of axis deviation). When the axis deviation occurs between the direction conversion gear mechanisms on the left and right upper rails, the upper rails cannot be slidden smooth or noises are generated with the rotational operation of the mechanisms. In the fourth patent document, the flexible cable is employed to serve as rotation transmission rod, so that the axis deviation is absorbed by the flexing of the cable to suppress the rotation-caused noises. However, the flexible cable capable of transmitting rotational power is expensive.